Effects of hydrogen addition on combustion, thermodynamics and emission performance of high compression ratio liquid methane gas engine

Abstract It is a potential approach to improve the fuel efficiency that the liquid methane gas (LMG) purified from liquefied natural gas (LNG) is fueled with the high compression ratio (CR) engine, while the actual effect is restricted by the low combustion velocity of methane. To solve this problem and further improve the LMG engine performance, the approach of hydrogen addition to LMG engine was investigated by combining experiment with numerical simulation. Based on experimental data, the computational fluid dynamics (CFD) model coupled with reduced chemical kinetic mechanism was built and calibrated, which was then employed to study the effects of different hydrogen energy fraction (HEF) on combustion, thermodynamic and emission of LMG engine. The results show that, the peak of heat release rate (HRR) increases sharply with the HEF rising and leads the maximum in-cylinder pressure to increase. The indicated thermal efficiency of LMG engine first increases and then decreases, and the maximum falls in the HEF range between 8% and 12%. Although the combustion velocity of mixture gas is obviously increased by hydrogen addition, the detonation trend still becomes larger and it increases by 10 times as HEF changes from 12% to 20%. As the HEF increases from 0 to 20%, NOx emission increases continuously, while CO and CH4 emissions decrease due to the higher combustion temperature. All these provided direction for improving LMG engine performance, and offered theoretical basis for selecting technology routes to meet emission regulations.